1. Field of the Invention
The present invention relates to a scanning electron microscope (SEM) alignment method and a scanning electron microscope.
2. Description of the Related Art
One factor used to describe capabilities of an SEM is a resolving power. The resolving power indicates the minimum distance between two distinguishable points. For the purpose of acquiring an image with a higher resolving power, it is necessary to align the optical axis of the SEM. The optical axis of the SEM is aligned chiefly through axis alignment and astigmatism correction. Both the axis alignment and the astigmatism correction are performed on a standard sample installed in the specimen stage, or on an observation target sample, for the purpose of reducing work of the operator. Recently-emerging technologies enable an SEM to perform automatic axis alignment and astigmatism correction through its self-evaluation of an optimal condition of its own. For example, Japanese Patent Application Publication No. 2003-22771 (corresponding to U.S. Pat. No. 6,864,493) describes a technology for automatic axis alignment which uses an image processing technology. In addition, Japanese Patent Application Publication No. 2000-195453 describes a technology for detecting misalignment of the optical axis on the basis of change in the path of an electron beam while the electron beam is scanned.